1. Field of the Invention
The present invention relates to tires suitable for motorcycles that run on uneven terrain such as mountain forests and wilderness.
2. Description of the Background Art
In uneven terrain, a road surface is uneven. When a motorcycle runs on the road surface, vibration is conveyed to the motorcycle. A load on a tire is low during normal running. The tire is required to exhibit vibration absorption under a low load.
A motorcycle running on uneven terrain repeats jumping and landing. A heavy load is applied to the tire upon landing. The tire is required to exhibit a high stiffness under a heavy load. A tire that exhibits a high stiffness under a heavy load is less likely to be twisted and squeezed upon landing. Further, in the tire, a so-called “snake bite” by a rim is less likely to occur. The “snake bite” refers to a phenomenon in which a tire is excessively deformed and portions of an inner surface of the tire abut against each other.
A crosslinked rubber having a high hardness needs to be used for a tread in light of traction performance. Motorcycle tires for uneven terrain are known in which a tread rubber and a sidewall rubber are formed of the same rubber material. In the tire, the sidewall rubber inevitably has its hardness increased. The tire exhibits poor vibration absorption under a low load.
Japanese Laid-Open Patent Publication No. 2008-285081 describes a motorcycle tire for uneven terrain in which sidewalls are softer than a tread. In the tire, vibration can be absorbed by the sidewalls that are soft. Japanese Laid-Open Patent Publication No. 2010-195059 also describes a motorcycle tire for uneven terrain in which a sidewall rubber and a tread rubber are formed of different rubber materials.
Japanese Laid-Open Patent Publication No. 2011-57184 describes a motorcycle tire for uneven terrain in which a rubber reinforcing layer is provided under a carcass. In the tire, the rubber reinforcing layer enables a high stiffness under a heavy load to be obtained.
The entire contents of these publications are incorporated herein by reference.